1. Field of the Invention
The present invention relates to an elastic wave device including a LiNbO3 substrate with elastic waves, and preferably plate waves, propagating through the LiNbO3 substrate.
2. Description of the Related Art
Various elastic wave devices have been proposed. In an elastic wave device described in International Publication No. WO2013/021948 A1 uses a LiNbO3 substrate. On both surfaces of the LiNbO3 substrate, IDT (interdigital transducer) electrodes are provided. Alternating voltages of the same phase are applied to the IDT electrodes provided on both the surfaces. SH waves in a zero order mode are used thereby as plate waves.
Japanese Unexamined Patent Application Publication No. 2010-220204 discloses a Lamb wave device using a piezoelectric thin film made of LiNbO3. Also in the Japanese Unexamined Patent Application Publication No. 2010-220204, IDT electrodes are formed on both surfaces of the LiNbO3. Japanese Unexamined Patent Application Publication No. 2010-220204 also discloses a structure in which an IDT electrode is provided on one surface of the piezoelectric thin film, and another electrode made of a metal film is provided on the other surface so as to be opposed to the IDT electrode. According to Japanese Unexamined Patent Application Publication No. 2010-220204, waves in a high-order mode having an acoustic velocity of 5000 m/second or more are excited as Lamb waves in the piezoelectric thin film.
In the elastic wave device described in International Publication No. WO2013/021948 A1, the IDT electrodes are formed on both the surfaces of the LiNbO3 substrate. This allows an increase in an electromechanical coupling coefficient of the SH waves in the zero order mode. Thus, a fractional bandwidth is increased.
However, an acoustic velocity is low, e.g., 3000 m/s to 4000 m/second. To increase a frequency, a wavelength λ is required to be short. Therefore, it becomes difficult to form the IDT electrodes and the like.
On the other hand, in the elastic wave device according to Japanese Unexamined Patent Application Publication No. 2010-220204, a high acoustic velocity of 5000 m/second or more is obtained. Thus, a high frequency is easily obtained. However, Japanese Unexamined Patent Application Publication No. 2010-220204 does not describe a structure in which a wide bandwidth and a high acoustic velocity are compatible.